Method of preparing manganese dioxide for dry cell

ABSTRACT

This invention relates to a method of preparing manganese dioxide with excellent battery performances, wherein naturally occuring manganese dioxide ores are employed as starting material and partially converted in air or oxygen at an elevated temperature and subsequently re-oxidized with a mixed solution of sulfuric acid and sodium or potassium chlorate.

United States Patent Miyazaki et a1.

[ Feb. 8, 1972 [54] METHOD OF PREPARING MANGANESE DIOXIDE FOR DRY CELL[72] lnventors: Kazuhide Miyazaki; Seiichi Tozawa, both of Tokyo, Japan[73] Assignee: Mitsui Mining & Smelting Co., Ltd.,

Tokyo, Japan [22] Filed: Aug. 6, 1969 211 Appl. No.: 847,947

[30] Foreign Application Priority Data Jan. 28, 1969 Japan ..44/5692[52] US. Cl ..23/145, 136/139, 75/80 [51] Int. Cl. ....C01g 45/02, HOlm15/00 [58] Field ofSearch...... .....136/139, 107, 138; 23/145;

[56] References Cited UNITED STATES PATENTS 1,305,250 6/1919 Burgess..136/139 Primary Examiner-Anthony Skapars Attorney-Woodhams, Blanchardand Flynn ABSTRACT This invention relates to a method of preparingmanganese dioxide with excellent battery performances, wherein naturallyoccuring manganese dioxide ores are employed as starting material andpartially converted in air or oxygen at an elevated temperature andsubsequently re-oxidized with a mixed solution of sulfuric acid andsodium or potassium chlorate.

5 Claims, 7 Drawing Figures PATENTEDF EB 6 I972 SHEET 3 [IF 3 i 6 HEAVYDISCHARGE CURVE min 1 COMMERCIALLY AVAILABLE g CHEMICAL MANGANESEDIOXIDE 5 2 MANGANESE DIOXIDO IN THE PRESENT INVENTION Q I0 E oRIGINALoRE 0.8: 0.75

5 I I0 I5 20 DURATION OF DISCHARGE (hr) LIGHT DISCHARGE CURVE 409-4? JMANGANESE DIOXIDO 5 IN THE PRESENT INVENTION COMMERCIALLY AVAILABLE 3cHEMIcAL MANGANESE DIOXIDE 6H2 R j 0 h ORIGINAL oRE uJ O l l I I 50 I00I50 200 DURATIONOF DISCHARGE (hr) METHOD OF PREPARING MANGANESE DIOXIDEFOR DRY CELL BACKGROUND OF THE INVENTION I. Field of the Invention Thisinvention relates to a method of preparing manganese dioxide havingimproved battery performance in high yield at a low cost from naturallyoccuring manganese dioxide ores, wherein roasting is performed topartially convert said ores into a lower oxide or oxides to a limitedextent, and then the roasted ores are treated with a hot aqueoussolution of a chlorate and sulfuric acid.

2. Description of the Prior Art Some of the conventional methods ofpreparing manganese dioxide for dry cell use by chemical process, whichhave hitherto been developed and suggested for commercial production,are mentioned in the following:

1. Thermal decomposition process of manganese nitrate:

MnNO heating MnO NO Manganese dioxide prepared by this method has lowactivity and also the resulting N gas is hazardous as well as corro-SIVe.

2. Oxidation process of manganese hydroxide by air or an oxidizingagent:

Mn(OII) O2 or an oxidizing agent MnO Penetration of air, oxygen, ozoneor an oxidizing agent into the interior of manganese hydroxide particlesis incomplete. Accordingly oxidation is not performed sufficiently andthe process is not suitable for dry cell use.

3. Oxidation process of manganese sulfate by an oxidizing agent:

In addition to chlorate, hypochlorite, permanganate and peroxide areprovided as an oxidizing agent. When the divalent manganese salts areused as starting material, the yield of manganese dioxide with thisprocess is very low and a large excess of an oxidizing agent is requiredin order to increase the yield.

4. Disproportionation process of suboxides with sulfuric acid:

The process has long been applied to the activation of manganese dioxideores of low activity but has a fault that approximately half thequantity of manganese must be eluted.

When used as a depolarizer in a dry cell, the manganese dioxide exhibitsunsatisfactory cell properties.

In addition to the processes l-4, many other methods including onewherein manganese chloride is thermally decomposed are proposed;however, all of these methods have seldom been practiced except theprocess 4 because of the aforementioned difficulties such as low yield,reduced oxidizing efficiency, high cost, and unsatisfactory cellproperties.

SUMMARY OF THE INVENTION The object of the present invention is toprovide methods of preparing manganese dioxide having excellent cellproperties at high yield and low cost by means of a simple process froma naturally occuring manganese dioxide ore whose cell properties are notgood enough to be used in the dry cell.

This invention relates to method of preparing manganese dioxide havingexcellent cell properties by treating the roasted ore, which is obtainedby roasting a naturally occuring manganese dioxide ore havinginsufficient performance for dry cell use in the presence of air oroxygen for a short period, by use of a hot aqueous solution of chlorateand sulfuric acid. According to the method provided in the presentinvention, manganese dioxide having excellent cell properties can beobtained at high yield and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS In FIGS. 1 and 2, is shown an electronphotomicrograph (X 5,000) of manganese dioxide prepared according to thepresent invention, while FIG. 3 shows the one by the conventionalchemical process.

FIG. 4 and FIG. 5 show the discharge curves to compare the physicalproperties of manganese dioxide prepared according to Example I withthose of other manganese dioxides, FIG. 4 showing heavy discharge curvesand FIG. 5 light discharge curves.

In FIG. 6 and FIG. 7, are shown discharge curves of manganese dioxideobtained according to Example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The shortcomings in theconventional processes are principally based on the facts that;

1. All of manganese contained in the raw material must be oxidized,

2. Half the quantity of manganese was eluted in some of the processes,e.g., the aforementioned process 4, and

3. They are applicable only to high grade manganese dioxide ores.

The inventors have found that utility factor of MnO in dry celldischarge reactions are only in the order of 20-40 percent and themajority of MnO in the interior of manganese dioxide particles remainunused for the reaction.

Therefore, a most essential point to improve the cell performances of agiven manganese dioxide will be summarized as involving the elevation ofthe utility factor of MnO in dry cell discharge reaction, especially howto activate the surface layer of manganese dioxide particles andutilization of MnO in the interior of manganese dioxide particles.

This will also lead to saving the amount of oxidizing agent and thusreduce the cost in the process.

More particularly, the present invention specifies a process wherein anaturally occuring manganese dioxide ore whose cell properties areunsatisfactory is roasted in the presence of air or oxygen for a shortperiod and the product is then reoxidized with a hot aqueous solution ofchlorate and sulfuric acid.

In the conventional methods, manganese dioxide ores of such highmanganese dioxide content as approximately percent or more are usuallyused while according to the present invention manganese dioxide orescontaining as low as about 60 percent manganese dioxide can be alsoutilized as raw materials. When roasting, reduction initiates at thesurface of manganese dioxide particles at approximately 450 C., and thusmanganese dioxide begins to change to a suboxide. In practicing thepresent invention, it is advisable for roasting to limit the reductionof manganese dioxide particles only to their surface since it is ratherdisadvantageous to reduce the very inner part of said particles.Therefore it is necessary to adjust the roasting temperature within therange of 450 to 700 C. and to adjust the time in consideration of theforegoing fact during the roasting process. For instance, when theroasting is conducted at the temperature of 450 C., it is desirable tofinish the roasting within 6 hours or thereabout. At the temperature of550 or 700 C. it is desirable that the processing period is individuallywithin 5 or 7 hours. If the roasting is continued any longer, thereduction goes on toward the inside of the manganese dioxide particles,which affects the later process unfavorably.

As the next step, the roasted particles thus obtained are then treatedwith a hot aqueous solution of a chlorate and sulfuric acid. In thisstep, suboxide in the surface layer of the manganese dioxide particleswhich has once been reduced in the roasting process is now reoxidizedand at the same time unreduced manganese dioxide in the interior of themanganese dioxide particles is also activated. In conducting theoxidation, an intensive oxidizing agent is required, and it ispreferable to use a hot aqueous solution consisting of a chlorate andsulfuric acid. The use of hypochlorite, permanganate and peroxide otherthan chlorate are unadvisable in practising the present invention, sincehypochlorite and peroxide work too weak in oxidization. Althoughpermanganate has a strong oxidization effect, the cell properties ofmanganese dioxide thus obtained are not satisfactory. As for chlorate,sodium and potassium salts are usually used. The quantity of theoxidizing agent in the present invention will be much less than inconventional processes because only the suboxides on the surface layerof the roasted manganese dioxide particles are necessary to bereoxidized.

Electron photomicrographs reveal that the manganese dioxide particlesprepared according to the conventional chemical oxidation processcomprise spherical or similarly shaped crystals having relatively largediameter, while the manganese dioxide particles prepared according tothis invention consist mainly of very fine needlelike crystals, as shownin FIGS. 1 and 2. The improved discharge properties in FIG. 4 and FIG.may be due to the above-mentioned difference in the shape of individualparticles. The suboxide formed in the surface layer of the roastedparticles is reoxidized immediately after having been immersed in theoxidizing solution to be reformed into needlelike manganese dioxide ofhigh activity. The manganese dioxide still remaining undecomposed in theinterior of individual particles is also activated without receiving anychemical change to be made into fine particles of irregular shape. Thequantity of manganese dioxide component eluted is very small comparedwith the conventional activation processes.

In the present invention the consumption of an oxidizing agent to beused in oxidation step has been minimized and at the same time a productmuch superior in quality to conventional ones is economically obtainableat high yield through the simplified process.

The following examples show the preferred embodiments of the presentinvention; however, the invention is not intended to be limited by thedetails set forth in these examples.

Example 1 Ten kilograms of a naturally occuring manganese dioxide ore of85 percent manganese dioxide grade was roasted in the presence of oxygenin the rotary kiln at 700 C. for 30 minutes. A solution was prepared byadding 1.6 kg. of concentrated sulfuric acid and 2.7 kg. of sodiumchlorate to 30 L. of water and heated up to 70 C., when the roasted orewas put into the solution, whose temperature was further raised to 90 C.The oxidizing process was continued for another 3 hours. When theprocess was completed, the treated ore was filtered while the solutionwas still hot, washed with water, dried and disintegrated, thus 9.5 kg.of the final product was obtained.

D-size Leclanch-type cells were constructed using the manganese dioxidethus obtained and compared with the original ore and another manganesedioxide commercially available for use in the dry cell, and thedischarge curves were plotted in FIG. 4 and FIG. 5.

Both FIG. 4 and FIG. 5 present the discharge curves plotted on the graphof the duration of the discharge (on the axis of abscissas) vs. the cellvoltage (on the axis of ordinates) and in FIG. 4 is shown the heavydischarge curves and in FIG. 5 the light discharge curves. As clearlyunderstood from those figures, the cell made of manganese dioxideprepared according to this invention shows its discharge capacity up to0.75 v. is improved by approximately 30-50 percent as compared withthose made of the original ore and other chemically synthesizedmanganese dioxide.

Cell

Heavy discharge Light discharge Ten kilograms of a naturally occuringmanganese dioxide ore of 75 percent manganese dioxide grade was roastedin a muffle furnace for 1 hour. A solution of sodium chlorate andsulfuric acid prepared according to Example I was heated up to 85 C.,when the roasted ore was put therein and heating was continued at thesame temperature for 4 hours. The slurry was filtered while it was stillhot, washed with water and dried to provide 9.33 kg. of the finalproduct.

FIG. 6 and FIG. 7 shows the D-size Leclanch cell performances of theproduct of Example 2.

Cell Heavy discharge Light discharge capacity capacity (made of) (downto 0.75 v.) (down to 0.75 v.)

(hours) (hours) Manganese dioxide prepared according to I) 220 thepresent invention: Commercially available chemical manganese I4 I70Original ore: I2 I40 What we claim is:

1. A method for preparing manganese dioxide comprising needlelikemanganese dioxide particles capable of imparting improved dischargecapacity when used in a dry cell, which comprises the steps of:

a. roasting fine particles of naturally occuring manganese dioxide orein an ambient atmosphere at a temperature ranging from 450" to 700 C.for a period of time sufficient to convert manganese dioxide in thesurface layer of said particles into manganese suboxides withoutconverting the inner portion of said particles;

. reacting the resultant roasted particles with a hot aqueous solutionof a chlorate salt and sulfuric acid to oxidize said manganese suboxidesto manganese dioxide; and

. separating the formed manganese dioxide particles comprisingneedlelike manganese dioxide from the hot aqueous solution, and thenwashing with water said separated manganese dioxide.

2. A method according to claim I, wherein ,said naturally occuringmanganese dioxide ore is one containing more than 60 percent manganesedioxide.

3. A method according to claim 2, wherein said naturally occuringmanganese dioxide ore is one containing between 60 and percent manganesedioxide.

4. A method according to claim 1, wherein said chlorate salt is a memberselected from the group consisting of sodium chlorate and potassiumchlorate.

5. A method according to claim I, wherein the manganese suboxideincluding in the roasted particles is oxidized with a hot aqueoussolution of sodium chlorate and sulfuric acid.

2. A method according to claim 1, wherein said naturally occuringmanganese dioxide ore is one containing more than 60 percent manganesedioxide.
 3. A method according to claim 2, wherein said naturallyoccuring manganese dioxide ore is one containing between 60 and 80percent manganese dioxide.
 4. A method according to claim 1, whereinsaid chlorate salt is a member selected from the group consisting ofsodium chlorate and potassium chlorate.
 5. A method according to claim1, wherein the manganese suboxide inCluding in the roasted particles isoxidized with a hot aqueous solution of sodium chlorate and sulfuricacid.